The Hammersmith & City line is a London Underground line that runs between Hammersmith in west London and Barking in east London. Printed in pink on the Tube map, it serves 29 stations over 15.8 miles (25.5 km). Between Farringdon and Aldgate East it skirts the City of London, the capital's financial heart, hence the line's name. Its tunnels are just below the surface and are a similar size to those on British main lines. Most of the track and all stations are shared with either the District, Circle, or Metropolitan lines.

The line's depot is at Hammersmith, close to Hammersmith station, built by the Great Western Railway to be operated by the Metropolitan Railway when the joint railway was electrified in the early 20th century. Sidings at Barking and near High Street Kensington (Triangle Sidings) stable trains overnight. Sidings at Farringdon were used during the C stock era; due to the greater length of the new S stock trains, these are no longer in use.